Flat-panel displays are widely used to visually display information where the physical thickness and bulk of a conventional cathode ray tube is unacceptable or impractical. Portable electronic devices and systems have benefitted from the use of flat-panel displays, which require less space and result in a lighter, more compact display system than provided by conventional cathode ray tube technology.
The invention described below is concerned primarily with field emission flat-panel displays. In a field emission flat-panel display, an electron emitting cathode plate is separated from a display face or faceplate at a relatively small, uniform distance. The intervening space between these elements is evacuated. Field emission displays have the outward appearance of a CRT except that they are very thin. While being simple, they are also capable of very high resolutions. In some cases they can be assembled by use of technology already used in integrated circuit production.
Field emission flat-panel displays utilize field emission devices, in groups or individually, to emit electrons that energize a cathodoluminescent material deposited on a surface of a viewing screen or display faceplate. The emitted electrons originate from an emitter or cathode electrode at a region of geometric discontinuity having a sharp edge or tip. Electron emission is induced by application of potentials of appropriate polarization and magnitude to the various electrodes of the field emission device display, which are typically arranged in a two-dimensional matrix array.
Field emission display devices differ operationally from cathode ray tube displays in that information is not impressed onto the viewing screen by means of a scanned electron beam, but rather by selectively controlling the electron emission from individual emitters or select groups of emitters in an array. This is commonly known as "pixel addressing."
It is important in field emission displays that the particle emitting surface of the electrode emitting cathode plate and the opposed display face be insulated from one another by a small distance across the full area of the display face. This is required to prevent electrical breakdown between the emitting surface and the display face. Furthermore, the spacing must be precisely uniform to assure uniform resolution, focus, and brightness.
In addition to uniform spacing of the display elements, it is also important to maintain the quality of the high vacuum typically required within such displays. According to the present invention, this is accomplished by providing of a getter in open communication with the evacuated space separating the particle emitting surface and the opposed display face. A getter is a chemically active substance such as metallic barium which removes traces of gas from otherwise evacuated spaces.
Many prior art field emission flat-panel displays use glass cathode plates. The invention described below, however, preferably utilizes a silicon or semiconductor substrate for its cathode or emitter plate. This allows conventional semiconductor processing techniques to be used in forming individual cathodes and addressing circuitry.
U.S. Pat. No. 4,923,421 to Brodie et al. describes one prior art display device utilizing a silicon cathode plate in a flat-panel display. Such has a transparent faceplate and a semiconductor backplate upon which cathodes are formed. The space between the faceplate and the backplate is evacuated. One problem with a device such as this is the maintenance of the required parallel spacing between the cathode plate and the faceplate. This problem is the result of the high vacuum inside the structure. This tends to bow the relatively thin semiconductor backing plate inward. To prevent such bowing, Brodie proposes a plurality of spacers interspersed between cathodes. While effective, such spacers are difficult to fabricate and interfere with cathode formation and placement.
Another problem with using a silicon backplate or cathode plate in conjunction with a glass faceplate is the difficulty of forming an adequate seal between the silicon and the glass for purposes of maintaining a vacuum within the display structure. Even when this problem is solved, valuable silicon real estate must be used for completing the seal. This reduces the number of cathode plates which can be fabricated from a single semiconductor wafer, and therefore adds to the cost of the display subsystem.
Further, present flat-panel display technology does not adequately address the problem of establishing electrical connections to the internal electrode circuits of a flat-panel displays. While the Brodie patent mentions "through-the-wafer" connections, these connections are difficult to manufacture and are detrimental to maintaining the desired vacuum within the flat-panel display.
The invention described below addresses each of the problems noted above, while achieving a simplicity which has been absent from prior designs.